We all know that Yelp can sometimes be a fair-weather friend to restaurants. One day you're riding high, earning serious praise from citizen reviewers -- and then just as fast, your restaurant's reputation can get hammered by one unhappy customer. We think the tactic employed by Joe Dough Sandwich Shop's sign-writer is pretty fantastic. Way to make lemonade out of lemons, you guys.

“Everyone with a computer is a damn food critic. Love this restaurant's sense of humor about it...” said Instagram user luxuryprgal, one of the many entertained people passing this photo around.

A blog post on the SFWeekly website this week brought a troubling Yelp-related incident to light. A Yelper claimed, falsely, to be a writer for SFWeekly in a restaurant review. SF Weekly's Food editor caught the lie and contacted the reviewer; she admitted that she actually wrote for SF Weekly Voice, and said she'd ask Yelp to change the review. But the website refused to amend the review -- a representative told SF Weekly that the lie in question was "personal opinion."

So many restaurateurs and publicists post glowing reviews of their own restaurants that Eater has a whole column dedicated to sniffing out shilly reviews.

People do all sorts of weird things when they know they're unidentifiable -- which can throw off the average on sites like Yelp, which rely on the forthrightness and honesty of strangers.

Because of said anonymity, there's not even any guarantee that a Yelper has visited the restaurant they're reviewing. One infamous case of this sort of fraud took place in Graham Elliott's Grahamwich restaurant in Chicago -- one Yelper gave it a vicious one-star review before it even opened.

Yelp has been criticized in the past for the byzantine methods it uses to sort reviews on a given restaurant's page. According to the site's FAQ, "Yelp's default sort order takes a number of factors into account and reflects our own attempt to present reviews in a meaningful order. For example, we'll favor reviews from your friends and the users you follow. The sort algorithm does not take into account whether the business is an advertiser or not." Thanks, Yelp. That clarifies literally nothing.

According to some reports, the "Yelp sort" has an insidious monetary element. Yelp salespeople have been known to call restaurants offering to push bad reviews far down in the list, if they'll agree to pay to advertise.

There are no guidelines on Yelp for what different star ratings mean -- one person's five star experience could be a jaded gastronaut's three star. Yelp does release the distribution of stars actually given out -- and they're definitely slanted toward the positive.

Many more people read Yelp than actually write reviews. Most reviewers fall into two categories: people who review every restaurant they visit (see the next slide for more on the "Yelp Elite") and those who have an extreme reaction. People probably won't review a restaurant if they thought it was just OK -- but they are likely to review it if they have very good or very bad experiences, making it hard to trust any given review.

If you're one of those people who writes a Yelp review of every nail salon and yakitori joint you visit, you can become part of the "Yelp Elite." Once you're part of this creme-de-la-creme, you can get invited to special "Elite-only" parties that restaurants throw to attract good reviews. Sounds nice, right? It may be, for the "Yelp Elite" -- but it's bad for the general public, because these events often translate into glowing, misleading reviews for the party-throwing restaurants.